The present invention relates to wireless communication networks and particularly to increasing the channel capacity of cellular networks.
Cellular fixed networks are generally formed of a plurality of base transceiver stations (BTSs) which wirelessly contact mobile units (referred to also as mobile stations and/or cellular handsets), serviced by the network. The BTSs are connected, usually in a tree topology, to a regional base station controller (BSC) which controls the routing of calls in the network. In the tree topology, one or more of the BTSs are connected directly to the BSC, and the other BTSs connect to the BSC through other BTSs which serve as relay units. The links of the tree are formed of cables which comprise a predetermined number of channels according to the capacity of the link. Each channel includes bandwidth sufficient for passing the signals of a single telephone call at the rate of 16 Kbit/sec. A commonly used link is the E1 link which includes 120 channels. Alternatively, each channel includes bandwidth sufficient for passing the signals of a single telephone call at the rate of 8 Kbit/sec, and in such a case an E1 link includes 240 channels.
When a mobile unit participates in a telephone call, the BSC allocates, using circuit switching, a connection from the BSC to the BTS servicing the mobile. The allocated connection is formed of dedicated channels which are used only for signals passed to and from the mobile unit to which the connection was allocated, and the allocation remains in effect until the telephone call is terminated. During the call, the mobile unit converts input signals into digital signals. As the use of wireless bandwidth is very costly, the digital signals are compressed by the mobile unit, and the compressed signals are transmitted to the servicing BTS. Generally, every 20 msec the mobile unit generates a packet of 320 bits which represents the sounds collected by the mobile unit during a time period of 20 msec.
The servicing BTS passes the compressed signals as they are, without decompressing them, to the BSC, over the mobile""s dedicated channels. The BSC usually decompresses the signals and transfers them to a Mobile switching Center (MSC) or to a public network to which the signals are directed.
Generally, each packet comprises a header and a payload. Exemplary headers are formed of 8 synchronization bits and 24 control bits or of 16 synchronization bits and 16 control bits. It is noted that other header structures exist, including encapsulations which distribute the control bits throughout the packets.
With the increase in usage of cellular phones the number of calls carried out concurrently by a single BTS and the number of concurrently allocated channels on a single link increased substantially. As the signals sent from the BTSs to the BSC are already compressed, further compression would degrade the signals below current quality standards.
Therefore, in order to supply the demand, additional cables and/or cables of larger bandwidth must be laid between the BSC and the BTSs. In some densely populated areas the laying of cables may be very costly.
An aspect of some preferred embodiments of the invention relates to identifying needless packets which are being passed over a connection the needless packets carry data which will not be used by the entity (e.g., BSC, BTS, mobile unit) to which the packets are directed. The data of these packets is not sent over the connection, thus reducing the load on the links hosting the connection. The needless packets are generated, for example, by a mobile unit or BTS in order to represent the sound signals at a time when the user of the mobile unit is not generating sounds (e.g., the user is listening to another party participating in the call).
Preferably, each link serves as one or more tunnels which pass packets from a plurality of mobile units assigned to the tunnel. Each tunnel is assigned a number of connections larger than the number of channels in the tunnel, based on the statistical average percentage of needless packets.
Packets passed through a tunnel are passed on one or more of the channels of the tunnel which channels are selected irrespective of the source, contents and destination of the packet. Thus, packets from a single source to a single destination which are passed through a tunnel may pass through different channels of the tunnel, and packets from different sources and to different destinations may pass on the same channel of the tunnel. In a preferred embodiment of the invention, each packet header is tagged with an identity tag which states to which connection the packet belongs, as the channel on which the packet is passed does not identify the channel. Alternatively or additionally, signaling bits not attached to the packets are used to state the connections to which the packets belong.
In a preferred embodiment of the invention, the needless packets are identified according to control bits in their header. Alternatively or additionally, the needless packets are identified based on control signals sent on a signaling line corresponding to the link on which the packets are passed. Further alternatively or additionally, the needless packets are identified based on their contents, e.g., packets which are all xe2x80x981xe2x80x99s.
An aspect of some preferred embodiments of the present invention relates to a base transmission station (BTS) which has an amount of bandwidth for receiving packets greater than the amount of bandwidth it has on links for forwarding packets. Preferably, the BTS and/or an external compression unit statistically compress the received packets onto the links it uses for forwarding packets.
There is therefore provided in accordance with a preferred embodiment of the invention, a method of forwarding signals over a cellular link, including receiving, at a first base station of a cellular fixed network, a packet of signals having a data payload directed to a second base station, determining whether the data payload will be used by the second base station, and forwarding the entire packet if the data payload will be used and not forwarding the entire packet if the data payload will not be used.
Preferably, receiving the packet includes receiving a stream of packets of the same size at equal intervals of time. Alternatively, receiving the packet includes receiving a packet which includes coded digital voice signals. Preferably, determining whether the data payload will be used by the second base station includes determining whether the contents of the payload will be decoded.
In a preferred embodiment of the invention, determining whether the data payload will be used by the second base station includes determining whether the second base station will forward the contents of the payload. Alternatively or additionally, determining whether the data payload will be used is dependent on information retrieved from a signaling line corresponding to the link. Alternatively or additionally, determining whether the data payload will be used is dependent on information retrieved from a header of the packet. Alternatively or additionally, determining whether the data payload will be used is performed before forwarding any part of the packet.
Alternatively, determining whether the data payload will be used is performed after forwarding at least part of the packet. Preferably, not forwarding the entire packet if the data payload will not be used includes forwarding less than the entire packet. Preferably, forwarding less than the entire packet includes forwarding only a header of the packet. Preferably, forwarding the entire packet includes forwarding through a tunnel used by a plurality of connections.
In a preferred embodiment of the invention, not forwarding the entire packet if the data payload will not be used includes not forwarding any of the packet. Preferably the method includes forwarding a message in place of a plurality of packets not forwarded.
In a preferred embodiment of the invention, forwarding the entire packet includes forwarding the packet along with a connection indication field. Alternatively or additionally, forwarding the entire packet includes forwarding through a tunnel used by a number of connections greater than the number of channels in the tunnel.
In a preferred embodiment of the invention, the first base station and the second base station include base transmission stations. In a preferred embodiment of the invention, the first base station includes a base station controller.
There is also provided in accordance with a preferred embodiment of the invention, a method of forwarding signals over a link between base stations, including receiving, at a first base station of a cellular fixed network, a plurality of packets, and forwarding the entire packet of at least one of the packets and not forwarding the entire packet of at least one of the packets. Preferably, receiving the plurality of packets includes receiving packets of a plurality of mobile units the packets of each mobile unit being received at a fixed rate. Alternatively or additionally, forwarding the entire packet of at least one of the packets includes forwarding the entire packet of less than a predetermined percentage of the received packets.
There is also provided in accordance with a preferred embodiment of the invention, a method for decompressing packets being forwarded over a link between base stations, including receiving signals belonging to a plurality of connections, forwarding packets which were received in their entirety, and generating replacement packets in place of packets not received in their entirety.
There is also provided in accordance with a preferred embodiment of the invention, apparatus for compressing packets being forwarded over a link between base stations, including an input interface which receives packets having a data payload, a processor which determines whether the data payload carries meaningful information, and an output interface which forwards the entire packet if the data payload carries meaningful information and does not forward the entire packet if the data payload does not carry meaningful information. Preferably, the processor which determines whether the data payload carries meaningful information also generates the packets. Alternatively or additionally, the processor examines a header of the packets to determine whether the data payload is meaningful.
In a preferred embodiment of the invention, the output interface begins to forward the packets before the processor determines whether the data payload is meaningful.
In a preferred embodiment of the invention, the apparatus includes a delay unit which delays forwarding the packets while the processor determines whether the data payload is meaningful.
There is also provided in accordance with a preferred embodiment of the invention, apparatus for decompressing packets being transmitted over a link between base stations, including an input interface which receives signals belonging to a plurality of connections, a forwarding unit which forwards packets which were received in their entirety, and a processor which generates replacement packets in place of packets not received in their entirety. Preferably, the processor generates replacement packets from received headers. Alternatively or additionally, the processor generates a plurality of replacement packets based on a single message. Preferably, the processor generates a plurality of replacement packets of different connections based on a single message.
There is also provided in accordance with a preferred embodiment of the invention, a system for forwarding packets from and to mobile units, including a base transmission station which generates a stream of packets each having a data payload, a compression unit which determines whether the data payload carries meaningful information, forwards the entire packet of packets which carry meaningful information and does not forward the entire packet of packets which do not carry meaningful information, and a base station controller which receives the forwarded packets and generates replacement packets for packets not forwarded in their entirety.
There is also provided in accordance with a preferred embodiment of the invention, apparatus for forwarding packets through a fixed cellular network, including a base transmission station having an interface to mobile units which receives packets of up to a total first amount of bandwidth, one or more first links, having a total second amount of bandwidth, through which the base transmission station receives packets, and one or more second links, having a total third amount of bandwidth which is smaller than the sum of the first and second amounts of bandwidth, through which the base transmission station forwards packets. Preferably, the third amount of bandwidth is smaller than the second amount of bandwidth. Alternatively or additionally, the base transmission station statistically compresses the packets received through the interface of the mobile units and through the one or more first links, into the second links.
In a preferred embodiment of the invention, a compression unit external to the base transmission station statistically compresses the packets received through the interface of the mobile units and through the one or more first links, into the second links.
There is also provided in accordance with a preferred embodiment of the invention, a telecommunication system operative in a cellular network, including one or more first base stations, each connected to a second base station via first transmission paths having first bandwidths, where said first bandwidths may be equal or different from each other, and a third base station connected to said second base station via a second transmission path having a second bandwidth which is substantially lower than the sum of said first bandwidths.